1. Field of the Invention
The present invention relates to an optical glass, an optical element, and an imaging lens.
2. Description of Related Art
In a photographic-imaging lens, a single lens made of a high-dispersion glass with an Abbe number (νd) of about 24 is combined with a single lens made of a low-dispersion glass so as to correct chromatic aberration.
Example 1 of Patent Document 1 discloses a zoom lens having a convex meniscus lens at a 3rd location from an object side towards an image side, the convex meniscus lens being made of a glass having an Abbe number (νd) of 23.78 and a refractive index (nd) of 1.84666 and being 3.5 mm in central thickness.
Numerical Example 2 of Patent Document 2 discloses an inner focus-type telescopic lens having a concave meniscus lens at a 4th location from an image side towards an object side, the concave meniscus lens being made of a glass having an Abbe number (νd) of 23.78 and a refractive index (nd) of 1.84666 and being 1.0 mm in central thickness.
The first Example of Patent Document 3 discloses a zoom telescopic lens having a convex meniscus lens with a central thickness of 5.5 mm and a concave meniscus lens with a central thickness of 2.94 mm at 7th and 11th locations from an object side towards an image side, respectively, both the lenses being made of a glass having an Abbe number (νd) of 23.8 and a refractive index (nd) of 1.84666.
Numerical Example 2 of Patent Document 4 discloses a zoom telescopic lens having a lens at an 8th location from an object side towards an image side, a location nearest to the image side in the state of being inserted into a magnification-conversion optical system, and the like, the lens being made of a glass having an Abbe number (νd) of 23.9 and a refractive index (nd) of 1.84666 and being in the range of 1.90 to 3.79 mm in central thickness.
In order to further enhance the function of such an imaging optical system or make the imaging optical system more compact, it is effective to further reduce the Abbe number of the high-dispersion lens or to increase the refractive index thereof.
Moreover, Patent Document 5 discloses an optical glass that is higher in dispersion than the glasses constituting the high-dispersion lenses disclosed in Patent Documents 1 to 4.